Podcast
Questions and Answers
The chemical shift range for alkyl hydrogens (C-H) is ______ ppm.
The chemical shift range for alkyl hydrogens (C-H) is ______ ppm.
0.5–2.0
In an NMR spectrum, a CH3 group in ethanol appears as a ______ due to its coupling with the CH2 group.
In an NMR spectrum, a CH3 group in ethanol appears as a ______ due to its coupling with the CH2 group.
triplet
The chemical shift for aldehyde hydrogens (C-H=O) is typically found between ______ ppm.
The chemical shift for aldehyde hydrogens (C-H=O) is typically found between ______ ppm.
9.0–10.0
To analyze NMR spectra, one must look at the number of peaks, chemical shifts, and ______ patterns.
To analyze NMR spectra, one must look at the number of peaks, chemical shifts, and ______ patterns.
An ester functional group can be identified in an IR spectrum by the presence of a ______ peak.
An ester functional group can be identified in an IR spectrum by the presence of a ______ peak.
In 13C NMR, each peak represents one set of equivalent ______ atoms.
In 13C NMR, each peak represents one set of equivalent ______ atoms.
In 1H NMR, peak intensity indicates the number of equivalent ______ atoms.
In 1H NMR, peak intensity indicates the number of equivalent ______ atoms.
Solvents used in NMR must not contain ______ atoms to avoid interference.
Solvents used in NMR must not contain ______ atoms to avoid interference.
TMS, or ______, is used as a standard for calibrating NMR spectra.
TMS, or ______, is used as a standard for calibrating NMR spectra.
Chemical shift (δ) is a measure of how much the magnetic field experienced by a nucleus differs from ______.
Chemical shift (δ) is a measure of how much the magnetic field experienced by a nucleus differs from ______.
In 1H NMR, neighboring inequivalent H atoms can cause ______, leading to peak splitting.
In 1H NMR, neighboring inequivalent H atoms can cause ______, leading to peak splitting.
A singlet in NMR indicates there are ______ neighboring H atoms.
A singlet in NMR indicates there are ______ neighboring H atoms.
The relative intensity ratios for a triplet in NMR is ______:2:1.
The relative intensity ratios for a triplet in NMR is ______:2:1.
Flashcards
NMR Chemical Shift Range for Aldehyde H
NMR Chemical Shift Range for Aldehyde H
Aldehyde hydrogens (C-H=O) appear in the 9.0-10.0 ppm range in a proton NMR spectrum.
NMR Chemical Shift Range for Alkyl H
NMR Chemical Shift Range for Alkyl H
Alkyl hydrogens (C-H) typically appear in the 0.5-2.0 ppm range in a proton NMR spectrum.
Spin-Spin Splitting in NMR (Ethanol)
Spin-Spin Splitting in NMR (Ethanol)
The number of neighboring protons influences the splitting pattern in NMR spectra. A CH3 group next to a CH2 group results in a triplet for CH3 and a quartet for CH2.
Ester Functional Group (NMR Characteristic)
Ester Functional Group (NMR Characteristic)
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NMR Integration and Peak Area
NMR Integration and Peak Area
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13C NMR
13C NMR
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1H NMR
1H NMR
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Equivalent Hydrogen Atoms
Equivalent Hydrogen Atoms
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Chemical Shift (δ)
Chemical Shift (δ)
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Spin-Spin Coupling
Spin-Spin Coupling
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Splitting Rule
Splitting Rule
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Integration Trace
Integration Trace
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TMS
TMS
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Study Notes
NMR Spectroscopy
-
Types of NMR:
- 13C NMR: Detects carbon atoms. Only a small percentage of carbon atoms are 13C
- 1H NMR: Detects hydrogen atoms. The intensity of peaks relates to the number of hydrogen atoms.
-
Solvents:
- Solvents without hydrogens are essential.
- Examples include CCl4 (non-polar) and CDCl3 (polar)
- CDCl3 gives a characteristic peak
-
TMS (Tetramethylsilane):
- Standard for calibration in both 1H and 13C NMR.
- Single, sharp peak, far from organic component peaks.
- Non-toxic
- Low boiling point
-
Chemical Shift (δ, ppm):
- Measures the difference between the magnetic field experienced by a nucleus and TMS.
- Measured in parts per million (ppm).
- Electronegative atoms increase shift (deshielding).
13C NMR Chemical Shift Ranges
- 5-40 ppm: Alkanes (C-C or C-H bonds).
- 50-90 ppm: C bonded to O.
- 160-185 ppm: Carbonyl carbons (C=O).
1H NMR Key Concepts
- Equivalent Hydrogens: Same signals in the spectrum.
- Intensity (Integration): Area under a peak= number of equivalent hydrogens.
- Spin-Spin Coupling (Splitting):
- Neighboring inequivalent hydrogens cause splitting.
- Splitting rule: Number of peaks = Number of neighboring H’s + 1.
- Example: 3 neighboring hydrogens ⇒ Quartet (4 peaks)
1H NMR Splitting Patterns
- Singlet (1 peak): No neighboring hydrogens.
- Doublet (2 peaks): 1 neighboring hydrogen.
- Triplet (3 peaks): 2 neighboring hydrogens.
- Quartet (4 peaks): 3 neighboring hydrogens.
1H NMR Integration Ratios (Pascal's Triangle)
- Doublet: 1:1
- Triplet: 1:2:1
- Quartet: 1:3:3:1
1H NMR Chemical Shift Ranges (ppm)
- 0.5-2.0 ppm: Alkyl hydrogens (C-H).
- 2.0-3.0 ppm: Hydrogens near electronegative groups(ex: C=O,C≡C)
- 3.0-4.5 ppm: Hydrogens bonded to C-O.
- 4.5-6.5 ppm: Hydrogens in alkenes (C=C).
- 6.5-8.0 ppm: Hydrogens in aromatic rings.
- 9.0-10.0 ppm: Aldehyde hydrogens (C-H=O).
- 10.0-12.0 ppm: Hydrogens in carboxylic acids (O=C-O-H).
Example: Ethanol (CH3CH2OH)
- CH3 (a): Triplet (2 neighboring H's; 0.7–1.2 ppm, integration = 3)
- CH2 (b): Quartet (3 neighboring H's; 3.7–4.1 ppm, integration = 2)
- OH (c): Singlet (no coupling; 0.5–5.0 ppm, integration = 1)
NMR Analysis Steps for Identifying Compounds
- Determine the Empirical Formula (elemental analysis).
- Find the Molecular Formula (mass spectrometry).
- Identify Functional Groups (IR spectroscopy).
- Analyze NMR Spectra (peak numbers, shifts, splitting).
Example: Compound Analysis (C8H16O2 Ester)
- Molecular formula: C8H16O2
- IR spectrum: C=O peak, no O-H peak ⇒ ester
- 1H NMR peaks:
- δ = 0.9 ppm (Singlet, area 9) ⇒ 3 equivalent CH3 groups.
- δ = 4.0 ppm (Quartet, area 2) ⇒ CH2 group adjacent to CH3.
- δ = 2.2 ppm (Singlet, area 2) ⇒ CH2 group adjacent to C=O.
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